“The doctrine of sincere cooperation limited our action in foreign affairs even if nominally we were still free.
“And if you want a monument of our freedom at the moment, it is the extraordinary leadership the Prime Minister has given over Ukraine which I think he simply would not have been able to do had we had to go along with and exercise our rights and our influences through a combined EU mechanism.”
Britain has been praised by US retired General David Petraeus for being the first to provide anti-tank weapons and anti-ship missiles to Ukraine in its defence against the Russian invasion.
General Petraeus also said that the UK had gone harder than any other country with sanctions against Russia and Putin’s regime.
Last week Boris Johnson and Foreign Secretary Liz Truss were banned from travelling to Russia by Putin in retaliation for the UK’s leading help for Ukraine.
Putin had already defined Mr Johnson as “Russia’s number 1 enemy”.
Ukraine’s President Zelensky had also praised Mr Johnson’s efforts and urged other European countries to follow his example.
Even before the British Prime Minister visited Kyiv, President Zelensky had insisted he set the standard for other countries to meet.
He said: “The leadership of the United Kingdom, in providing our country with all the necessary assistance in terms of defence, as well as leadership in sanctions policy, will go down in history forever.”
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The diplomat said: “Let’s be honest we saw it with the vaccine and now with Ukraine. Britain outside the EU is more nimble and able to make decisions more quickly.
“With the coronavirus vaccine you [the UK] were able to get it agreed and rolled out weeks before the EU.
“It is the same with this crisis. The UK saw the threat first and was starting to prepare sanctions and other actions before the rest of Europe.”
The diplomat added: “Some in the EU complain that Britain is trying to bounce the EU into action too quickly.
“But if it had not been for that then we would be seeing the issue [Ukraine] discussed in endless committee meetings with no resolution. Too often that’s the EU way.”